Implementing a package of essential non-communicable diseases interventions in low- and middle-income countries: a realist review protocol.

INTRODUCTION: The burden of non-communicable diseases (NCDs) is increasing rapidly, particularly in low- and middle-income countries (LMIC), accounting for 85% of premature deaths in the region. LMICs have been facing an increasing trend of a double burden of disease (infectious diseases and NCDs) that has led to multiple challenges in prioritising strategies for NCDs control amidst limited resources. Evidence indicates that measures such as the WHO's package of essential non-communicable (PEN) diseases interventions can prevent and control NCDs. However, because of the complexity of such health interventions, there is limited evidence that explains how the intervention works, for whom and in what context. We aim to unpack the causal mechanisms explaining how, why, for whom and in what context PEN prevents and controls NCDs.

METHODS AND ANALYSIS: We propose a realist review to understand how, why, for whom and under what circumstances PEN works or does not work. The review process includes five steps applied iteratively throughout the study: clarification of review scope, searching for evidence, appraising and extracting data, synthesising evidence and drawing conclusions, and disseminating the findings. Programme theories will be developed using the realist logic for theory formulation-Retroductive Theorising. The context-mechanism-outcome (CMO) heuristic tool will be used to develop the programme theories. Portions of the reviewed documents describing constructs of context, mechanism and outcomes will be coded inductively and extracted. These extracted constructs will then be linked abductively to formulate CMO configurations.

ETHICS AND DISSEMINATION: Formal ethical approval is not required for this review. Study findings will be disseminated through publications in peer-reviewed journals, conference presentations and formal and informal reports.